The global continental water budget using GRACE spaceborne gravimetry and high-resolution consistent geodetic-hydrometeorological data analysis

GRACE重力测量提供了大陆上储水量变化的直接测量。因此，这项新技术首次能够在大尺度上关闭大陆水平衡。我们建议利用GRACE重力测量技术直接从大流域的地面降水和流量测量中确定大尺度的实际蒸散发。该项目还将通过储存变化和排放提供以前无法获得的对大型流域大气湿度通量的直接测定。因此，它可以对大气模式数据进行新的评估。然而，传统GRACE产品的各向异性误差结构限制了它们的实用性，即使是在最大的可用盆地。水文准信号出现在不存在信号的地区，例如沙漠。为此，我们开发了一种新的GRACE误差建模方法，该方法利用了已知的质量变化及其不确定性，这些变化来源于选定区域的水文约束，例如，可以忽略不计的输入（沙漠）或可以忽略不计的蒸散（雪/冰，高海拔地区）。该策略允许在常规去混叠程序之外对重力信号进行校正，从而提高空间、时间和质量方面的分辨率。密切的跨学科合作将确保GRACE成为可靠的水文传感器。我们对大尺度实际蒸散发和大气水分通量特征的研究使我们能够预测未测量流域的排放量，并利用GRACE数据评估相应的不确定性。因此，全球覆盖计量和未计量流域的数据将有助于以最少的模式假设，更好地确定全球大陆和各自的大气水收支。

GRACE gravity measurements provide a direct measure of water storage changes over continents. Thus, this novel technique enables¿for the first time¿to close the continental water balance on large scales. We propose to use GRACE gravimetry to directly determine large scale actual evapotranspiration from ground-based measurements of precipitation and discharge on large basins. The project will also provide a previously not available direct determination of atmospheric moisture fluxes on large basins from storage changes and discharge. As such, it enables a novel evaluation of atmospheric model data. However, the anisotropic error structure of conventional GRACE products is limiting their utility even for the largest basins available. Hydrological quasi-signals appear in areas, e.g. deserts, where no signal exists. To this end, we develop a new approach to GRACE error modelling, that makes use of known mass changes and their uncertainties, derived from hydrological constraints for selected areas, e.g. with negligible inputs (deserts) or with negligible evapotranspiration (snow/ice -, high altitude regions). This strategy allows for a correction of the gravity signal beyond the conventional de-aliasing procedures and thus an improvement of resolution in terms of space, time and mass. The close interdisciplinary collaboration will ensure the establishment of GRACE as a reliable hydrological sensor. Our investigations of the characteristics of both the large scale actual evapotranspiration and the atmospheric moisture flux enable us to predict discharge from ungauged basins and to evaluate the corresponding uncertainty by use of GRACE data. The global coverage of data from gauged and ungauged basins will hence lead to an improved determination of the global continental and the respective atmospheric water budget with a minimum of model assumptions.